Driving With Propane
From inside the Roush-modified F-150, there's nothing to tip you off that you're driving a propane-powered truck. It drives like its gas-burning counterpart in almost every respect, except how it starts. When you key the ignition, the gauges come to life and the radio turns on, but nothing else happens. If it's cold out, the fuel system takes up to ten seconds to pressurize. Then, once it's darn good and ready, the starter motor magically engages and the truck fires. (On warmer days, or when the engine is at operating temperature, the starting sequence requires less than three seconds.)
The truck quickly settles into an idle that's just as smooth as that of the standard 5.4-liter Ford V-8. It sounds the same, too. Importantly, the powerplant doesn't exhibit any cold-blooded characteristics, and the truck can be driven away from the curb as quickly as the driver moves the shifter into D.
On the road, my initial concerns about carrying 59 gallons of fuel above the axles are quickly allayed. The Super Crew Cab is designed to haul more than 1700 pounds of payload; LP weighs 4.23 pounds/gallon, so a full tank weighs less than 250 pounds. The truck's handling and braking capabilities aren't stressed by the new fuel system, and we confirmed this during a week of driving.
Spending so much time behind the wheel gave us the chance to evaluate Roush's revised programming for the engine control module. Often, modified vehicles have advantages in some dynamic tests but suffer in normal driving situations. Not so with the Roush truck. Very gentle throttle applications generated very smooth acceleration. Jumping on the right pedal launched the truck with authority, and there were no flat spots in the acceleration. In a word, Roush's new powertrain calibrations are perfect.
Since Roush changed nothing else in the truck, our rear-wheel-drive XLT Super Crew performed exactly like a gasoline-powered 2008 F-150 in all other respects, including ride quality and quietness. In light of the recent launches of the 2009 Dodge Ram and the 2009 F-150, however, it's clear that the 2008 F-150 is getting old in terms of handling dynamics and ride refinement. At this time, Roush hasn't announced a conversion for 2009 F-150s.
Regarding fuel economy, the F-150 travels about 10 percent fewer miles per gallon on LP than on gasoline, so average driving delivers about 13 mpg. This loss is more than made up for by the lower cost of LP fuel, which usually tracks about 75 percent of the cost of gasoline. The net is that an LP F-150 costs less to run per mile than its gasoline-swilling counterpart.